In horticulture plant production greenhouses are often equipped with artificial light sources to extend the growing period of the plants, beyond the point where the sun has set. Furthermore, this allows a producer to bring plants on the market on demand, independent of the season. To achieve this aim normally high pressure sodium lamps (HPS) are used. However, this causes a number of problems. First of all, the supplemental light emission causes light pollution, annoying people who are living in the proximity of the greenhouse. To reduce the disturbance, shading devices are used which shade the illuminated inner part of the greenhouse from the surrounding. The shading devices may either cover the windows or are arranged above the planting area of the greenhouse. Furthermore, high pressure sodium lamps typically generate light in the green/yellow spectrum. However, the absorption spectra of most common pigments of plants are in a different frequency range.
As the “duty cycle” and the intensity of the sunlight often fluctuate, the artificial light sources are not only used to extend the growing period but also to achieve a constant illumination of the plants. Therefore, the shading device is not only prohibiting the flow of the artificial light into the surrounding but also the intrusion of sunlight into the greenhouse.
In the GB 2 396 252 A a textile fabric is disclosed, comprising surface mounted LEDs and connective tracks. The connective tracks, which may be yarns woven in the fabric or printed on the fabric, are connected with the LEDs. To drive the LEDs, an electrical current is flowing through the conductive tracks. Unfortunately, the described textile fabric absorbs the heat of the sun. Furthermore, the interwoven electrical yarns are difficult and expensive to produce.
Thus, the invention has for its object to eliminate the above mentioned disadvantages. In particular, it is an object of the invention to provide a shading device for a greenhouse, which on the one hand protects the plants within the greenhouse from environmental impacts and on the other hand illuminates the plants.